OS Structures

• SPIN paper
  • What features of Modula-3 are essential for implementing the extensibility features of SPIN? Why?
• Exokernel paper
  • A library OS implements a paged virtual memory on top of Exokernel. An application running in this OS encounters a page fault.

    Walk through the steps from the time the page fault occurs to the resumption of this application.

    Make any reasonable assumptions to complete this exercise (stating the assumptions).

• Liedtke paper
  • Sketch how you will implement a device driver (say for a simple device like a keyboard; if you are really adventurous do for a disk) using the primitives provided by Liedtke's microkernel.

    [Hint: Assume address space A0 magically exists that exposes the physical memory. Assume the device registers are memory mapped at some well known physical addresses in high memory.]

  • What is the difference between a "thread" as defined in Liedtke's paper and a Strand in SPIN?
• Xen Paper
  • Imagine a Linux OS top of Xen (XenoLinux). A user launches an application "foo" on top of XenoLinux. Walk through the steps that happen before foo actually starts running.
  • foo starts executing; it executes a blocking system call

    fd = fopen("bar");

    • (a) Show all the interactions between XenoLinux and Xen for this call Clearly indicate when foo resumes execution.

    Upon resumption, foo executes another blocking system call

    fwrite(fd, bufsize, buffer);

    • (b) Show all the interactions between XenoLinux and Xen for this call Clearly indicate when foo resumes execution.

    Don't worry about the exact syntax of the above calls.

  • Construct and analyze a similar example for network transmission and reception by foo.
  • All processes in XenoLinux occupy the virtual address space 0 through VMMAX, where VMMAX is some system defined limit of virtual memory per process.

    XenoLinux itself is a protection domain on top of Xen and contains all the processes that run on top of it.

    Given this how does XenoLinux provide protection of processes from one another? [Hint: Work out the details of how the virtual address spaces of the processes are mapped by XenoLinux via Xen.]